1. Field of the Invention
The present invention generally relates to designing a differential amplifier capable of working with a reduced voltage power supply.
2. Background Description
Historically, differential amplifiers require three stacked transistors for operation: a current source to set the quiescent DC bias, the input differential pair, and the load transistors. Complementary Metal Oxide Semiconductor (CMOS) transistors require a reasonable threshold voltage (typically 0.5 v) for proper operation. Since the sum of the threshold voltages of the three stacked devices exceeds one volt, this type of differential amplifier is not feasible for very low power supply voltages (&lt;1 V).
If the device thresholds were reduced to 0.2 v, a normal amplifier could work, but the dynamic range would be reduced to 0.4 v, and DC standby power would increase, which for many mobile battery applications would be unacceptable.